Shaun Merrigan's Information Pages


Category: Restoration


HP 3245A Capacitor Replacement

Posted by Shaun Merrigan in Electronics, Restoration, Test Equipment. Comments Off on HP 3245A Capacitor Replacement

4th January

The HP3245A Universal Source (datasheet is copyright HP/Agilent) is a precision AC/DC voltage and current source that can provide a wide range of precise and repeatable voltages and currents up to +-100vdc and 100mA dc. It can also provide sine, square and arbitrary waveforms up to 1Mhz and 200vpp. Such an instrument is extremely useful in the lab for calibrating meters, driving current and voltage amplifiers and checking equipment. The particular units I have were built in 1992/1993 which means the electrolytic capacitors are approaching 30 years of age. I had decided to replace the RIFA line filter capacitors in (documented here) both my units and performed routine power rail voltage and ripple checking as part of that. For example:

+5.0840 4.4mv+15.194 30mV+18.625 29mV-18.691 28mV

The other power rails and HV Amp power supply also measured good, using an … Read More »


RIFA Safety Capacitor Replacement in HP Gear

Posted by Shaun Merrigan in Electronics, Restoration, Test Equipment. Comments Off on RIFA Safety Capacitor Replacement in HP Gear

3rd January

In a previous post, I had documented the condition of several RIFA Y Safety capacitors, showing clearly the cracked condition of the outer case. This condition is a precursor to the well documented failure of this style of RIFA capacitor. Reportedly, these problems have been solved since Kemet squired RIFA in 2007. Of course the equipment which contains these potentially failing capacitors is typically older than 2007.

For example, I recently replaced six (two from each instrument) of these capacitors from the following equipment:

HP 3245A (1992)HP3245A (1992)HP 3458A (1989)

HP 3245A (1992) Original RIFA Safety Capacitors. The line filter is on the bottom right.

HP 3458A (1989) Original RIFA Safety Capacitors. The line filter cutout is on the bottom right.

Each and every RIFA Safety Capacitor I removed from this equipment showed cracks in the case.

Cracked RIFA … Read More »


Hickok 209A VTVM Restoration Part 7

Posted by Shaun Merrigan in Electronics, Restoration, Test Equipment. Comments Off on Hickok 209A VTVM Restoration Part 7

3rd January

I have completed the electrical restoration of one Hickok 209A VTVM. This included:

Replacing all the paper and electrolytic capacitorsReplacing all the carbon composition resistors (most were out of tolerance)Installing a polarized AC plug, line fuse and proper safety capacitorReplacing the meter movement (original was mechanically damaged)Rebuilding and restoring the battery holderBalancing the bridge tube resistorsGiving the unit a full check on all modes and ranges

With all of the above complete I can declare the unit ready to use. The cabinet still needs to be cleaned and refinished, but that will have to wait until warmer weather arrives and I can work outside.

The results of my testing were very interesting. I used my lab equipment (see below) to check the 209A on all of its ranges and modes (with the exception of the decibel range). … Read More »


RIFA Safety Capacitor Failures

Posted by Shaun Merrigan in Electronics, Restoration, Test Equipment. Comments Off on RIFA Safety Capacitor Failures

13th November

RIFA Safety Capacitor Failures have been documented by many of us who restore and maintain vintage electronics equipment. One very spectacular failure was caught live here: courtesy Dave Jones of the EEVBLOG. These capacitors were widely used in test equipment manufactured during the late 1980’s through the 1990’s. The general consensus is that the capacitors fail because the outer case (presumed to be a type of epoxy) develops cracks which allows moisture to penetrate into the body of the capacitor. This leads to internal short circuits which cause the capacitor to fail catastrophically. Because these capacitors are line to ground, they could see line voltage whenever a piece of equipment is plugged in, even when switched off. The crack network can develop to the point where large pieces of the outer case spall off, exposing … Read More »


Hickok 209A VTVM Restoration Part 6

Posted by Shaun Merrigan in Electronics, Restoration, Tech, Test Equipment. Comments Off on Hickok 209A VTVM Restoration Part 6

13th January

This is the sixth part of an “N” part series documenting my restoration of the Hickok 209A VTVM, SN 1333254.

Hickok 209A VTVM Restoration Part 6: Component replacement decisions

In this Part 6 of the series I will document the condition of the passive circuit components in the Hickok 209A VTVM, and justify why I decided to replace (or not replace) them.

Initial resistor and capacitor measurements Hickok 209A

Starting with the resistors, I measured 8 initially, and of those 5 were out of marked specification on the high side. One more was right at the high side specification and two were within specification. These were all 5% and 10% tolerance carbon composition resistors. Based on these data, I made the decision to replace all the 5% and 10% carbon composition resistors. I used 1% metal oxide resistors with … Read More »


Hickok 209A VTVM Restoration Part 5

Posted by Shaun Merrigan in Electronics, Restoration, Test Equipment. Comments Off on Hickok 209A VTVM Restoration Part 5

1st January

This the fifth part of an “N” part series documenting my restoration of the Hickok 209A VTVM, SN 1333254. Hickok 209A VTVM Restoration Part 5: Checking the meter movement.

This piece of test gear is all about the large, beautiful meter movement, so I need to determine if this one works properly. What I intend to do is connect the meter to a precision power supply and good ammeter through a current limiting resistor and then determine how the meter responds. The meter is supposed to be a 500uA full scale movement.

Here is the test setup:

Analog Meter Test Instrumentation Setup

A 10kohm limiting resistor is connected in series with the power supply. The power supply is a Tektronix PS5004 and the meter is a Tektronix DM5120.

Full Scale Deflection on the meter was about 497 uA:

Analog … Read More »


Hickok 209A VTVM Restoration Part 4

Posted by Shaun Merrigan in Electronics, Restoration, Test Equipment. Comments Off on Hickok 209A VTVM Restoration Part 4

1st January

This the fourth part of an “N” part series documenting my restoration of the Hickok 209A VTVM, SN 1333254. Hickok 209A VTVM Restoration Part 4: Restoring the battery holder.

In Part 3 of this series I documented the condition of the D Cell battery holder and outlined the restoration plan for the unit. The first step is to remove and restore the corroded battery holder.

Hickok 209A SN 133254 Corroded Battery Holder

Besides the obvious corrosion, the white connecting wire to the negative terminal was corroded under the insulation from the battery spring clip to the switch solder lug. I replaced the entire length of this wire. The other short wire and ring terminal were cleaned as described below.

Hickok 209A SN 133254 Corroded Terminal Wire

The process I used to restore the battery holder:

Desolder the two … Read More »